Many illnesses or conditions require administration of a constant or sustained level of a medicament or biologically active agent to provide the most effective prophylactic or therapeutic. This may be accomplished through a multiple dosing regimen or by employing a system that releases the medicament in a sustained fashion.
Attempts to sustain medication levels include the use of biodegradable materials, such as polymeric matrices, containing the medicament. The use of these matrices, for example, in the form of microparticles or microcarriers, provides sustained release of medicaments by utilizing the inherent biodegradability of the polymer. The ability to provide a sustained level of medicament can result in improved patient compliance.
However, these sustained release devices can exhibit high release of active agent over the first twenty-four hours, often referred to as a burst. In some instances this burst can result in an undesirable increase in the levels of biologically active agent and minimal release of agent thereafter. In addition, due to the high solution concentration of medicament within and localized around these sustained release devices, the medicament can aggregate thereby increasing immunogenicity in vivo and interfering with the desired release profile for the medicament.
Therefore, a need exists to exert additional control over the release profile of sustained release compositions by, for example, reducing the burst of agent and/or providing an improved release such as a longer period of release.